For a fine machining or processing such as, for example, etching, deposition, oxidation, or sputtering in a manufacturing process of a semiconductor device or a flat panel display (FPD), plasma is used to perform an excellent reaction on processing gas at a comparatively low temperature. Discharge is typically used for generating plasma. Plasma processing apparatuses are generally classified into a plasma processing apparatus using high-frequency discharge and a plasma processing apparatus using microwave discharge. High-frequency discharge systems are also classified into a capacitive-coupled system in which a parallel flat panel electrode is installed within a processing container and an inductive-coupled system in which a spiral or swirling electrode is attached around the processing container. Among several plasma generation systems, the capacitive-coupled system has become a mainstream of a device for mass production and a device for device development.
In the capacitive-coupled plasma processing apparatus, an upper electrode and a lower electrode are arranged in parallel within a pressure-reducible processing container or reaction container, an object to be processed, for example, a semiconductor wafer, is placed on the lower electrode, and high frequency waves having a predetermined frequency are applied to the upper electrode or the lower electrode through a matching unit. Electrons are accelerated by a high-frequency electric field generated by the high frequency waves, plasma is generated by dissociation and ionizing collision of the electrons, and molecules and atoms of the processing gas, and a desired plasma processing (for example, an etching process) is performed on a wafer surface by radicals or ions in the plasma.
In a plasma process, (in-plane) uniformity of the process is a basic requirement for improving yield, the importance of the (in-plane) uniformity gradually increases with the progress of miniaturization of the semiconductor device or an increase in diameter of the semiconductor wafer, and a required level thereof increases. In this regard, in a conventional capacitive-coupled plasma processing apparatus, the uniformity of the process significantly depends on uniformity of the density of plasma on the semiconductor wafer. Thus, researches have been repeatedly conducted into a structure of an electrode used for generating plasma, in particular, an electrode (high-frequency electrode) to which the high frequency waves are applied.
As one typical example, a capacitive-coupled plasma processing apparatus is known, in which an upper electrode facing a lower electrode where an object to be processed is placed is divided into an inner electrode and an outer electrode in a radial direction to variably control a ratio of high-frequency powers for generating plasma which are distributed to both electrodes (Japanese Patent Laid-Open Publication No. 2004-193566).
In the capacitive-coupled plasma processing apparatus, the outer upper electrode is electrically connected to an output terminal of a high-frequency power supply that outputs the high frequency waves for generating plasma through a tubular conductive member and the inner upper electrode is electrically connected to the output terminal through a rod type central conductive member. A variable condenser is inserted in the middle of the central conductive member, and as a result, capacitance of the variable condenser is variably controlled by, for example, a step motor.